ROM3 is the only one that succeeds as a children’s film while still resembling passable entertainment for adults. I’d still rank it among my least favorite Toho tokusatsu films, mostly because there’s still a lot of “fat” that could have been trimmed, but I think it’s easily the best and most enjoyable of the series.
The first two have that horrible cliche from bad kiddie movies where adults have to act as clueless idiots to show that the children better comprehend whatever fantasy world they’re inhabiting. In ROM3, the adult characters simply act to ensure their children’s safety, which in turn ties in with the movie’s theme (that all of courage, wisdom, and hope are necessary to combat hatred and evil). Similarly, the children aren’t know-it-all’s or even very annoying as they had been in the previous films.
Speaking of themes, I think this is the only film in the series in which Masami Suetani’s theme is organically integrated into the plot. He does so by having each of the major characters make logical sacrifices that both develop their characters and move the plot. It’s not advanced storytelling but it’s better than his inadequate work on the first two films.
Another major problem with the first two entries is that the monster content is dull, unimaginative, and impenetrable, especially so for ROM1. While it’s no Toho tokusatsu masterpiece, at least the sfx scenes in ROM3 are brief enough that they don’t stop the movie altogether. I wonder if they realized after two films of the same stuff that it’s really hard to dynamically film a puppet slamming into a suited actor and make it appear dramatic; they mostly avoided that kind of monster “battling” in this one.